Short answer, and probably not very helpful... It depends, they can be.

What products are you looking at? Many soluble fertilizers can simply be diluted and used for foliar feeding. There are often instructions on the packaging. If you are buying in person, it should say... but if you are buying from the web, try visit the Home Site for the manufacturer and check the specifications and instructions for use.

I looked at instructions and saw nothing about where to apply--just how much to use and when. I use all purpose miracle grow and super bloom for my patio annuals and fish emulsion for veggies, DLs, roses. Now that I don't need to plant so much, I am having more time to fertilize and that's how I started thinking whether water soluble automatically means it is for foliar apps.

Here's the MG page that mention's foliar feeding. While they do say it can be used for foliar feeding, they do not recommend foliar feeding house plants. They don't give a dilution ratio, so one would assume regular dilution. However, MG is basically a salt. So, if you decide to use it I would dilute it at least by half (I think 1/4 - 1/8 would even be better) then, then next day, I would wash it off with plain water. Keep in mind that when using soluble fertilizers very dilute solutions used more often (if necessary,) is usually better than the recommended amount. You can always add more a few days later if the plants don't seem to respond, but you can't take it back once it's on.

You can also foliar feed with the fish emulsion, but keep in mind that it is very strong, so it too should be heavily diluted, and it can stink lol. I would also wash that off in a day or 2.

Another thing to consider is that if you have pets they can be attracted to the fish emulsion and damage your plants, and they can be poisoned with the MG. Another reason to wash it off.

I don't see why you couldn't foliar feed with the super bloom, but I think I would use that just as recommended, just following the guideline of less is more. Remember, you can't take it back without heavy flushing.

whatever is in the foliar fertilizers is water soluble.. unless it's concentrated 95%+ of liquid in a fertilizer is water. this is why it's always more economical to buy dry water soluble fertilizer and add your own water because you're basically paying for the water.

personally, the only thing i would consider to apply to plant leaves is magnesium (epsom salt) every thing else is poorly absorb by the leaves. feeding is always best via their roots..

Hmmm, have never used ES for leaves, just around base of plants.

Im afraid I haven't posed my question clearly enough. What I want to know us whether you are supposed to apply water soluble ferts. on the foliage or at the base of the plant. I see nothing anywhere as to the WHERE to apply. The slow release is applied at the base of plant.

@rgreen. The link you provided says apply to both, Foliage and base. I always focused on foliage. I will apply on leaves and base and observe what happens.

Oh, I apologize bossy, I misunderstood. I thought you were looking to use them as foliar sprays. You can do as you see as appropriate, but I will say that in most cases, unless there are special circumstances, there is little reason to foliar feed.

The most common reason for me to foliar feed is when I am taking cuttings. The plants have no roots, so the only way to fertilize is though the foliage.

Other reasons I can see foliar feeding having benefits might be if you want to just give the plants a little 'pick me up', if you were concerned about salts building up in the soil, if you wanted to give the plants a fast boost for some reason, and... there are plants that may require foliar feeding because of their growth habits (but I deal mostly with the most common of house plants, and veggies.) So, as I said, cuttings are the only time that I foliar feed.

So, I would say, apply the fertilizer at the base of the plants at a more diluted ratio than the product recommends.

water soluble just means that the fertilizer dissolves in water, by no means it indicates it's exclusively for foliar feeding. generally, water soluble fertilizers are typically fed to plant roots.. but they can also be used to foliar feed as well (ie something marketed as a foliage fertilizer in a spray bottle).. i just don't think it's effective at all, especially things like fish emulsion (organic matter) which is typically not fully broken down (decomposed) so it's best to use something like fish emulsion in the soil as it breaks down over time and then become available to the plant to absorb via their roots. some people swear by foliage feeding, but the way i see it is when i am hungry i don't smear the food over my skin ;)

perhaps you should do an experiment. have two plants, feed one plant the water soluble fertilizer in the soil and the other on foliage. wait a month or two and observe results..

I might do that. I have two DLs side by side with which I can experiment

Is there such thing as non-water-soluble plant fertilizer?

Yes, alfalfa pellets, Ext released synthetics and organics, cottonseed burr,

Most organics are not water soluble - the exceptions are those which are presented in a liquid form and there are not too many of them: kelp/seaweed or fish emulsion and few newer, liquid formulations from Dr Earth and others.

Foliar fertilization is not at all an efficient method of providing plant nutrients - plants absorb very little via their foliage, water or fertilizer, so why waste your time and money? All ferts - liquid or granular, slow release or not - are best applied to the soil at the root zone, where they can be most easily taken up by the roots, which is how plants normally assimilate any needed nutrients.

Garde gal, I did not know that. Will change my ways. Thanks all, I'm glad I posted this ?

LOL... "I'm glad I posted this *? * "

With the question mark! Too funny. It's always good to learn. I often jump into discussions over my head just so I can learn. People sometimes get frustrated with me... but... too bad lol. Nothing ventured...

Any liquid fertilizer can be sprayed on the foliage. The main reason for doing this is with nutrients that are easily tied up by the soil. For example, Fe is strongly bound in alkaline soils. Applying directly to leaves bypasses the soil and can be much MORE efficient. Two caveats: it is easy to damage leaves by spraying too concentrated solutions (keep the total concentration below 1%) and plants can only absorb small amounts of nutrients through the leaves. That's why this method is used mostly for micronutrients. (And no, not everything is soluble - do a Google search for 'solubility product'.)

For anyone wanting to learn a lot more about foliar fertilization, check out: https://www.researchgate.net/publication/235609131_Foliar_Fertilization_Scientific_Principles_and_Field_Practices

Well said toxcrusadr.